The present disclosure relates to a signal processing apparatus, a signal processing method, and a program. More particularly, the disclosure relates to a signal processing apparatus, a signal processing method, and a program for detecting and correcting spectrum inversion in a more generalized manner than before.
At present, there exist two major modulation systems for terrestrial digital broadcasting: the orthogonal frequency division multiplexing (OFDM) system using numerous orthogonal carriers, and the single carrier system employing one carrier.
Typical terrestrial digital broadcasting standards that adopt the OFDM system include DVB-T (Digital Video Broadcasting-Terrestrial) and ISDB-T (Integrated Services Digital Broadcasting-Terrestrial).
The terrestrial digital broadcasting standards adopting the single carrier system may include ATSC (Advanced Television Systems Committee), DTMB (Digital Terrestrial Multimedia Broadcast), and DVB-C (Digital Video Broadcasting-Cable), for example.
In such setups of terrestrial digital broadcasting whereby received broadcast waves (received signal) are spectrally inverted for example, receiving apparatus may need to perform spectrum inversion for correct decoding.
Generally, transmitting apparatus transmits a signal by spectrally inverting either the upper or the lower frequency band in the frequency spectrum of the signal while leaving the other frequency band spectrally uninverted. Unless the spectrally inverted signal is perfectly symmetrical with the spectrally uninverted signal, the spectrally inverted signal generally needs to be spectrally inverted on the receiving side for correct decoding.
There are cases, however, that do not specify whether the transmitting side should perform spectrum inversion. For example, where different transmitting apparatuses spectrally invert different bands in the frequency spectrum upon transmission, the receiving apparatus may need to detect whether the received signal has been spectrally inverted. That is, if the received signal is found spectrally inverted, the receiving apparatus may spectrally invert the received signal; if the received is found spectrally uninverted, the receiving apparatus may not spectrally invert the received signal.
With the single carrier system, however, it may be difficult for the demodulation portion of the receiving apparatus to detect whether the received signal is spectrally inverted. In that case, if the transmitted signal (I, Q) is spectrally inverted, the received signal may be demodulated into (I, −Q) or (Q, I) when output on the receiving side before the signal is handed over to the error correction portion of the receiving apparatus. This can result in an erroneous decoding process.
There have been proposed methods for detecting the presence or absence of spectrum inversion and correcting the detected inversion (e.g., see Japanese Patent Laid-Open No. 2009-182552; called Patent Document 1 hereunder). The technique described in Patent Document 1 uses convolution code as error correcting code.